Civil Engineering Reference
In-Depth Information
TABLE 13.3
Common Types of Deep Foundations
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Topic
Discussion
Pile foundations
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End-bearing pile:
This pile's support capacity is derived
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principally from the resistance of the foundation material on
which the pile tip rests. End-bearing piles are often used
when a soft upper layer is underlain by dense or hard strata. If
the upper soft layer should settle, the pile could be subjected
to downdrag forces, and the pile must be designed to resist
these soil-induced forces.
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Friction pile:
This pile's support capacity is derived princi-
pally from the resistance of the soil friction and/or adhesion
mobilized along the side of the pile. Friction piles are often
used in soft clays where the end-bearing resistance is small
because of punching shear at the pile tip. A pile that resists
upward loads (i.e., tension forces) would also be considered
to be a friction pile.
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Combined end-bearing and friction pile:
This pile derives
its support capacity from combined end-bearing resistance
developed at the pile tip and frictional and/or adhesion resis-
tance on the pile perimeter.
Piles are usually driven into specific arrangements and are used
to support reinforced concrete pile caps or a mat foundation. For
example, the building load from a steel column may be supported
by a concrete pile cap that is in turn supported by four piles
located near the corners of the concrete pile cap.
Concrete-filled steel pipe piles
Another option is a concrete-filled steel pipe pile. In this case,
the steel pipe pile is driven into place. The pipe pile can be dri-
ven with either an open or a closed end. If the end is open, the
soil within the pipe pile is removed (by jetting) prior to place-
ment of the steel reinforcement and concrete. Table 13.4 pro-
vides additional details on the concrete-filled steel pipe piles.
Prestressed concrete piles
Table 13.4 presents details on typical prestressed concrete piles
that are delivered to the job site and then driven into place.
Other types of piles
Table 13.4 provides additional details on various types of piles.
Piers
A pier is defined as a deep foundation system, similar to a cast-
in-place pile, that consists of a columnlike reinforced concrete
member. Piers are often of large enough diameter to enable down-
hole inspection. Piers are also commonly referred to as drilled
shafts, bored piles, or drilled caissons.
Caissons
Large piers are sometimes referred to as caissons. A caisson can
also be a watertight underground structure within which work is
carried on.
Mat or raft foundation
If a mat or raft foundation is constructed below ground surface or
if the mat or raft is supported by piles or piers, then it should be
considered to be a deep foundation system.
Floating foundation
A floating foundation is a special type of deep foundation where
the weight of the structure is balanced by the removal of soil
and construction of an underground basement.
